1. Field of the Invention.
The present invention relates generally to medical devices, systems and methods, and more specifically to improved devices, systems and methods for creating an ablation zone in tissue. The device may be used to treat atrial fibrillation.
The condition of atrial fibrillation (AF) is characterized by the abnormal (usually very rapid) beating of the left atrium of the heart which is out of synch with the normal synchronous movement (“normal sinus rhythm”) of the heart muscle. In normal sinus rhythm, the electrical impulses originate in the sino-atrial node (“SA node”) which resides in the right atrium. The abnormal beating of the atrial heart muscle is known as fibrillation and is caused by electrical impulses originating instead in the pulmonary veins (“PV”) [Haissaguerre, M. et al., Spontaneous Initiation of Atrial Fibrillation by Ectopic Beats Originating in the Pulmonary Veins, New England J Med., Vol. 339:659-666].
There are pharmacological treatments for this condition with varying degrees of success. In addition, there are surgical interventions aimed at removing the aberrant electrical pathways from the PV to the left atrium (“LA”) such as the Cox-Maze III Procedure [J. L. Cox et al., The development of the Maze procedure for the treatment of atrial fibrillation, Seminars in Thoracic & Cardiovascular Surgery, 2000; 12: 2-14; J. L. Cox et al., Electrophysiologic basis, surgical development, and clinical results of the maze procedure for atrial flutter and atrial fibrillation, Advances in Cardiac Surgery, 1995; 6: 1-67; and J. L. Cox et al., Modification of the maze procedure for atrial flutter and atrial fibrillation. II, Surgical technique of the maze III procedure, Journal of Thoracic & Cardiovascular Surgery, 1995; 2110:485-95]. This procedure is shown to be 99% effective [J. L. Cox, N. Ad, T. Palazzo, et al. Current status of the Maze procedure for the treatment of atrial fibrillation, Seminars in Thoracic & Cardiovascular Surgery, 2000; 12: 15-19] but requires special surgical skills and is time consuming.
There has been considerable effort to copy the Cox-Maze procedure for a less invasive percutaneous catheter-based approach. Less invasive treatments have been developed which involve use of some form of energy to ablate (or kill) the tissue surrounding the aberrant focal point where the abnormal signals originate in the PV. The most common methodology is the use of radio-frequency (“RF”) electrical energy to heat the muscle tissue and thereby ablate it. The aberrant electrical impulses are then prevented from traveling from the PV to the atrium (achieving conduction block within the heart tissue) and thus avoiding the fibrillation of the atrial muscle. Other energy sources, such as microwave, laser, and ultrasound have been utilized to achieve the conduction block. In addition, techniques such as cryoablation, administration of ethanol, and the like have also been used.
There has been considerable effort in developing catheter based systems for the treatment of AF using radiofrequency (RF) energy. One such method is described in U.S. Pat. No. 6,064,902 to Haissaguerre et al. In this approach, a catheter is made of distal and proximal electrodes at the tip. The catheter can be bent in a J shape and positioned inside a pulmonary vein. The tissue of the inner wall of the pulmonary vein (PV) is ablated in an attempt to kill the source of the aberrant heart activity. Other RF based catheters are described in U.S. Pat. No. 6,814,733 to Schwartz et al., U.S. Pat. No. 6,996,908 to Maguire et al., U.S. Pat. No. 6,955,173 to Lesh, and U.S. Pat. No. 6,949,097 to Stewart et al.
Another source used in ablation is microwave energy. One such device is described by Dr. Mark Levinson [(Endocardial Microwave Ablation: A New Surgical Approach for Atrial Fibrillation; The Heart Surgery Forum, 2006] and Maessen et al. [Beating heart surgical treatment of atrial fibrillation with microwave ablation. Ann Thorac Surg 74: 1160-8, 2002]. This intraoperative device consists of a probe with a malleable antenna which has the ability to ablate the atrial tissue. Other microwave based catheters are described in U.S. Pat. No. 4,641,649 to Walinsky; U.S. Pat. No. 5,246,438 to Langberg; U.S. Pat. No. 5,405,346 to Grundy et al.; and U.S. Pat. No. 5,314,466 to Stem et al.
Another catheter based method utilizes the cryogenic technique where the tissue of the atrium is frozen below a temperature of −60 degrees C. This results in killing of the tissue in the vicinity of the PV thereby eliminating the pathway for the aberrant signals causing the AF [A. M. Gillinov, E. H. Blackstone and P. M. McCarthy, Atrial fibrillation: current surgical options and their assessment, Annals of Thoracic Surgery 2002; 74:2210-7]. Cryo-based techniques have been a part of the partial Maze procedures [Sueda T., Nagata H., Orihashi K. et al., Efficacy of a simple left atrial procedure for chronic atrial fibrillation in mitral valve operations, Ann Thorac Surg 1997; 63:1070-1075; and Sueda T., Nagata H., Shikata H. et al.; Simple left atrial procedure for chronic atrial fibrillation associated with mitral valve disease, Ann Thorac Surg 1996; 62: 1796-1800]. More recently, Dr. Cox and his group [Nathan H., Eliakim M., The junction between the left atrium and the pulmonary veins, An anatomic study of human hearts, Circulation 1966; 34:412-422, and Cox J. L., Schuessler R. B., Boineau J. P., The development of the Maze procedure for the treatment of atrial fibrillation, Semin Thorac Cardiovasc Surg 2000; 12:2-14] have used cryoprobes (cryo-Maze) to duplicate the essentials of the Cox-Maze III procedure. Other cryo-based devices are described in U.S. Pat. Nos. 6,929,639 and 6,666,858 to Lafintaine and U.S. Pat. No. 6,161,543 to Cox et al.
More recent approaches for the AF treatment involve the use of ultrasound energy. The target tissue of the region surrounding the pulmonary vein is heated with ultrasound energy emitted by one or more ultrasound transducers. One such approach is described by Lesh et al. in U.S. Pat. No. 6,502,576. Here the catheter distal tip portion is equipped with a balloon which contains an ultrasound element. The balloon serves as an anchoring means to secure the tip of the catheter in the pulmonary vein. The balloon portion of the catheter is positioned in the selected pulmonary vein and the balloon is inflated with a fluid which is transparent to ultrasound energy. The transducer emits the ultrasound energy which travels to the target tissue in or near the pulmonary vein and ablates it. The intended therapy is to destroy the electrical conduction path around a pulmonary vein and thereby restore the normal sinus rhythm. The therapy involves the creation of a multiplicity of lesions around individual pulmonary veins as required. The inventors describe various configurations for the energy emitter and the anchoring mechanisms.
Yet another catheter device using ultrasound energy is described by Gentry et al. [Integrated Catheter for 3-D Intracardiac Echocardiography and Ultrasound Ablation, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 51, No. 7, pp 799-807]. Here the catheter tip is made of an array of ultrasound elements in a grid pattern for the purpose of creating a three dimensional image of the target tissue. An ablating ultrasound transducer is provided which is in the shape of a ring which encircles the imaging grid. The ablating transducer emits a ring of ultrasound energy at 10 MHz frequency. In a separate publication [Medical Device Link, Medical Device and Diagnostic Industry, February 2006], in the description of the device, the authors assert that the pulmonary veins can be imaged.
While these devices and methods are promising, improved devices and methods for creating a heated zone of tissue, such as an ablation zone are needed. Furthermore, it would also be desirable if such devices could create single or multiple ablation zones to block abnormal electrical activity in the heart in order to lessen or prevent atrial fibrillation. It would also be desirable if such devices could be used in the presence of blood or other body tissues without coagulating or clogging up the ultrasound transducer. Such devices and methods should be easy to use, minimally invasive, cost effective and simple to manufacture.
2. Description of the Background Art.
Other devices based on ultrasound energy to create circumferential lesions are described in U.S. Pat. Nos. 6,997,925; 6,966,908; 6,964,660; 6,954,977; 6,953,460; 6,652,515; 6,547,788; and 6,514,249 to Maguire et al.; U.S. Pat. Nos. 6,955,173; 6,052,576; 6,305,378; 6,164,283; and 6,012,457 to Lesh; U.S. Pat. Nos. 6,872,205; 6,416,511; 6,254,599; 6,245,064; and 6,024,740; to Lesh et al.; U.S. Pat. Nos. 6,383,151; 6,117,101; and WO 99/02096 to Diederich et al.; U.S. Pat. No. 6,635,054 to Fjield et al.; U.S. Pat. No. 6,780,183 to Jimenez et al.; U.S. Pat. No. 6,605,084 to Acker et al.; U.S. Pat. No. 5,295,484 to Marcus et al.; and WO 2005/117734 to Wong et al.